By Liam Allen and James Kelly BBC News

Support groups are demanding action to stop it happening again.

Colette Lynch was stabbed to death by her estranged partner

Colette Lynch was killed by her ex-partner, Percy Wright, two days after he had smashed a window at her home in Rugby and threatened to "slit her throat".

The police were called but Wright - who was a delusional psychotic - was not arrested or sectioned.

Ms Lynch is not the first woman to come to harm at the hands of a violent ex-partner the police had been made aware of. Other high-profile cases include the murders of Hayley Richards and Tania Moore.

But domestic violence help groups want Colette Lynch to be the last and are demanding urgent reforms to ensure there are no repeats of the tragedy.

Sandra Horley is the chief executive of charity Refuge.

How many more women need to be killed before the police start to take their cries for help seriously? Sandra Horley Refuge

She said the case of Colette Lynch was a "shocking example" of insufficient protection for victims of domestic violence.

"Every week, two women in the UK die at the hands of current or former partners. Most of these deaths are predictable and preventable.

"How many more women need to be killed before the police start to take their cries for help seriously?

"To leave a woman begging for help, at the mercy of a dangerous man is deplorable."

She said Colette had become another "heartbreaking statistic" and called for "strong political and police" leadership.

Guidance 'not followed'

"I hope that her life, at least, will lead to some serious lessons being learnt," she added.

Nicki Norman is deputy chief executive of the Women's Aid Federation of England - a national charity working to end domestic violence against women and children.

She said the death of Colette Lynch was preventable and clear guidance on investigating cases of domestic violence, produced by the Association of Chief Police Officers (ACPO), was not always being followed by frontline officers.

The police are key to sending out a message that domestic violence is an unacceptable crime. Nicki Norman Women's Aid Federation

"This means that women experiencing domestic violence are often still reluctant to report to the police," she said.

"Every police response to domestic violence should include a thorough risk assessment and measures put in place to manage the risk of the perpetrator.

"Given that one in four women will experience domestic violence in their lifetime, the police are key to sending out a message that domestic violence is an unacceptable crime."

Harassment Act

Measures to tackle domestic violence and the harassment of women by ex-partners have been added in recent years.

Legislation was strengthened through the 1997 Protection from Harassment Act, which created a specific offence of stalking.

Tracey Morgan, chief executive of the Network for Surviving Stalking, said: "Every crime victim should be taken seriously but particularly in situations with ex-partners - let's try to prevent tragedies like this."

Tania Moore was murdered despite repeated appeals for protection

The Colette Lynch case has echoes of the murder of the show jumper Tania Moore in March 2004.

Mark Dyche, 36, plagued Ms Moore, 26, with chilling text messages and stalked her during a year-long hate campaign after she ended their engagement.

Ms Moore's ordeal continued despite several complaints to the police. Dyche shot her at point blank range after running her off a country lane near her home in Alkmonton, Derbyshire.

He was jailed for life for her murder after a trial in 2005.

Several officers were disciplined over the handling of events prior to the shooting. The IPCC described inquiries leading up to the killing of Ms Moore as "abysmal".

Tania Moore's mother Stella has since campaigned for the creation of a nationwide network of Family Justice Centres, which bring a range of agencies that help domestic violence victims under one roof.

'Improve training'

Europe's first Family Justice Centre opened its doors in Croydon in December 2005, based on a successful American model.

Mrs Moore said: "Tania went to the police station numerous times in the months prior to her death and they totally ignored her.

"I don't think domestic violence should be left to the police to deal with. I don't think a lot of it is taken seriously and I don't think police officers are trained well enough.

"Family Justice Centres will work with the police, immediately recognise the danger signs and can give protection. When we get more of these centres that's when murders will stop taking place."